Diamond coated dental bur machining of natural and synthetic dental materials

Diamond coatings are attractive for cutting processes due to their high hardness, low friction coefficient, excellent wear resistance and chemical inertness. The application of diamond coatings on cemented tungsten carbide (WC-Co) burs has been the subject of much attention in recent years in order to improve cutting performance and tool life. WC-Co burs containing 6% Co and 94% WC with an average grain size 1–3 micron were used in this study. In order to improve the adhesion between diamond and the bur it is necessary to etch away the surface Co to prepare it for subsequent diamond growth. Hot filament chemical vapour deposition (H.F.C.V.D.) with a modified vertical filament arrangement has been employed for the deposition of diamond films. Diamond film quality and purity has been characterised using scanning electron microscopy (S.E.M.) and micro-Raman spectroscopy. The performance of diamond coated WC-Co burs, uncoated WC-Co burs, and diamond embedded (sintered) burs have been compared by drilling a series of holes into various materials such as human teeth, and model tooth materials such as borosilicate glass and acrylic. Flank wear has been used to assess the wear rates of the burs when machining natural and synthetic dental materials such as those described above.     

C.V.D. Coating of Alumina Reinforcing Particles to Improve the Wear Resistance of H.S.S. Based Composites

C.V.D. coating of the reinforcing ceramic particles used in particulate metal matrix composites allows the control of reactivity at the particle/matrix interface. Wear resistant high speed steel-based composites containing uncoated A1₂0₃, uncoated TiC and C.V.D. coated A1₂0₃ were liquid phase sintered, then characterized using “pin-on-disc” wear testing. TiC or TiN C.V.D. coatings of A1₂0₃ were tested to determine die increase in reactivity of the particles with the liquid phases formed during sintering. This resulted in a porosity decrease at the particle/matrix interface in addition to a better ceramic/metal cohesion due to improved wettability. Reactivity and wettability were studied using differential thermal analysis, electron microprobe analysis, transmission electron microscopy, and image analysis. Results from pin-on-disc wear testing illustrated the role of the C.V.D. coating on the wear behavior of the studied materials. Lower wear rates were obtained with the composites containing TiC or TiN-coated Al₂0₃. These results showed that there is a relation between wettability of ceramic particles by the metallic phases and wear resistance of the composites.     

等离子原位合成Fe-Cr-V-C堆焊合金的耐磨性

采用等离子堆焊技术制备了不同Cr含量的Fe-Cr-V-C堆焊合金,借助扫描电镜和X射线衍射等分析手段研究了碳化物形貌及合金物相组成。同时研究了Cr含量对合金硬度和耐磨性的影响,并探讨了磨损机理。结果表明:堆焊合金组织由马氏体、铁素体、奥氏体、M7C3及VC组成。合金中随着Cr含量的提高,由于硬质相M7C3和VC的数量及形态变化不大,而具有高硬度的针状马氏体基体组织的减少使得合金的耐磨性先降低,当达到一定值后继续增加Cr含量,M7C3的数量逐渐增多,因而耐磨性随后增大;当Cr含量达到27.2%(质量分数)时,大量高硬度六边形M7C3复合物(约HV1200)结合一定量VC(约HV1600)颗粒构成坚实的耐磨骨架,使得合金具有最佳的耐磨性。     

过共晶高硼堆焊合金的显微组织及耐磨性

采用药芯焊丝埋弧堆焊方法制备含有0.1～1.0 C,4～13 Cr,2.5～3.2 V,2.2～3.8 B(质量分数/硼合金.借助光学显微镜、扫描电镜、X射线衍射等手段,研究其显微组织及硼化物分布形貌.结果表明:显微组织由铁素体+马氏体+残余奥氏体+M2B+M3(B,C)+V2C等组成,其初生M2B相的数量随硼含量而改...     

Tribological behavior of CrAlSiN/W2N multilayer coatings deposited by DC magnetron sputtering

The CrAlSiN/W₂N multilayer coatings were fabricated by DC magnetron sputtering. The bilayer periods of multilayer films were controlled in the range from 3 to 20 nm. The cross-sectional structure of multilayer and monolayer coatings was evaluated by transmission electron microscopy (TEM). The wear behavior of monolayer and multilayer coatings was investigated by a pin-on-disc tribometer. The nano-scratch tester was employed to study the crack propagation of scratched coatings. The images of wear scars were observed by optical microscopy (OM). The cross-sectional image of scratched films was analyzed by transmission electron microscopy (TEM). Owing to the nano-layered structure and higher hardness (or H/E ratio), the multilayer coatings exhibited better wear resistance than homogeneous films. The coefficient of friction of CrAlSiN/W₂N multilayer coating with a bilayer period of 8 nm was around 0.6, and that of CrAlSiN homogeneous film was about 0.8. Different crack propagation mechanisms of CrAlSiN/W₂N multilayer and CrAlSiN monolayer coatings were proposed and discussed.     

Microstructural evolution in lubricious ZnO films grown by pulsed laser deposition

Zinc oxide (ZnO) is well known to the electronic industry as a piezoelectric material. Recent research from this laboratory also indicates the potential of ZnO as a tribological material. The current work describes the evolution of microstructure with deposition parameters in pulsed laser deposited ZnO thin films, specifically targeted for friction and wear applications. Films were characterized by high resolution scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). Friction and wear measurements were made using a ball-on-disk tribometer. Films were grown in vacuum (V) as well as in 5 mTorr of oxygen (O₂), while the substrates were kept at room temperature (RT). The RT/V ZnO films have (002) columnar texture with an average column width of 20 nm. The RT/O₂ films also are nanoclumnar with (002) texture, but each column is a mosaic of low-angle boundaries. Deformation mechanisms associated with nanocrystalline grain structure were analyzed with particular reference to sliding contact. Mechanisms to provide the observed low friction of RT/O₂ films (μ=0.15–0.20) have been activated by its mosaic structure.     

Preparation and Characterization of MWCNTs/E44

Epoxy resin was modified by multi-walled carbon nanotubes（MWCNTs）with an in situ method.The composite was observed using scanning electron microscopy （SEM）and X-ray diffraction （XRD）,and its abrasive wear resistance and tensile properties were tested.The results show that the function groups found on the surface of MWCNTs helped to improve the resin＇s crack resistance,and the cracks were found notably reduced in the composite.Although the resin and MWCNTs were bonded physically ,the tensile properties and wear resistance of the composite were improved notably when an optimum amount of MWCNTs were filled in Epilote-44（E44）.When 5wt pct acidified MWCNTs were filled in E44,the elastic modulus ,breaking strength and wear resistance of the composite increase to 226.7%,303.3%and 272.55%（153.29%）,respectively.     

Hardness and grain size relations for thick chromium films deposited by hallow cathode discharge

Chromium films deposited by hollow cathode discharge show a variety of hardness, wear resistance and anti-corrosion characteristics. To find the relation between these properties and the film structure, investigations using X-ray diffraction, transmission electron microscopy and Auger electron spectroscopy were carried out for a variety of substrate bias voltages.Films deposited by hollow cathode discharge at 190°C and biased at 0 V and ?50 V and an electrochemically plated hard chromium film were compared by measurements of the Vickers microhardness and the line broadening of the (222)Cr line of X-ray diffraction after vacuum annealing at several temperatures. The hardness is approximately proportional to the square root of the line broadening.All the deposited films show a similar relation between hardness and line broadening. The square root of the grain size of these films as observed by TEM is inversely proportional to the hardness. This relation supports an empirical equation obtained by Agarwal et al. who worked with vacuum-deposited NiCr films. The grain size of the films as observed by TEM is several times larger than that calculated from line broadening.     

Tribological behaviour of mechanically synthesized titanium-boron carbide nanostructured coating

In this paper, titanium-boron carbide (Ti/B4C) nanocomposite coatings with different B4C nanoparticles contents were fabricated by surface mechanical attrition treatment (SMAT) method by using B4C nanoparticles with average nanoparticle size of 40 nm. The characteristics of the nanopowder and coatings were evaluated by microhardness test, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Friction and wear performances of nanocomposite coatings and pure titanium substrate were comparatively investigated, with the effect of the boron carbide content on the friction and wear behaviours to be emphasized. The results show the microhardness, friction and wear behaviours of nanocomposite coatings are closely related with boron carbide nanoparticle content. Nanocomposite coating with low B4C content shows somewhat (slight) increased microhardness and wear resistance than pure titanium substrate, while nanocomposite coating with high B4C content has much better (sharp increase) wear resistance than pure titanium substrate. The effect of B4C nanoparticles on microhardness and wear resistance was discussed.     

Mechanical wear behavior of nanocrystalline and multilayer diamond coatings on temporomandibular joint implants

We used microwave plasma chemical vapor deposition to deposit nanocrystalline and multilayer (nanocrystalline/microcrystalline/nanocrystalline) diamond thin films on Ti-6AI-4V substrates imitating the condyle and fossa components of the temporomandibular joint. We tested the condyle/fossa pairs for wear in a mandibular movement simulator for an equivalent of two years of clinical use. Analysis of the wear surfaces by optical microscopy, scanning electron microscopy (SEM), and Raman spectroscopy showed that damage in both the films was minimal, no loss of film occurred and the wear performance was superior for the multilayer film. Comparisons with an uncoated condyle/fossa pair showed that the coated temporomandibular joint pairs had improved wear performance.     

Characterization and tribological evaluation of duplex treatment by depositing carbon nitride films on plasma nitrided Ti-6Al-4V

Carbon nitride (CN_X) films (with N/C ratio of 0.5) were deposited on both untreated and plasma nitrided Ti-6Al-4V substrates by D.C. magnetron sputtering using a graphite target in nitrogen plasma. TEM and XPS analysis revealed the formation of both amorphous CN_X structure and crystalline -C₃N₄ phases in the deposited coatings. Nano-indentation tests showed that the film hardness was about 18.36 GPa. Both the scratch tests and indentation tests showed that compared with CN_X film deposited directly on Ti-6Al-4V, the load bearing capacity of CN_X film deposited on plasma nitrided Ti-6Al-4V was improved dramatically. Ball-on-disk wear tests under both dry sliding and lubricated conditions (with simulated body fluids) were performed to evaluate the friction and wear characteristics of the deposited coatings. Results showed that under both dry and lubricated conditions, the duplex treated system (i.e., with CN_X film deposited on plasma nitrided Ti-6Al-4V substrate) was more effective in maintaining a favorable low and stable coefficient of friction and improving wear resistance than both individual plasma nitriding and CN_X films on Ti-6Al-4V substrate. Under dry sliding conditions, the generated wear debris of spalled films were accumulated on the wear track, mechanically alloyed and graphitized, thus significantly reducing the coefficient of friction and preventing wear of the substrate. However, under lubricated conditions, due to the flowing of the fluids, the lubricating wear debris was taken away by the fluids, and therefore, the direct contact of two original surfaces resulted in high coefficient of friction and extensive abrasive wear of the substrate for CN_X films deposited on Ti-6Al-4V substrate. Also when there was some small-area spallation of CN_X films, the fluids could seep into the interface between the film and substrate, thus degrading the interfacial adhesion and resulting in a large area spallation.     

Si3N4和52100钢对磨副材料对CrN薄膜干摩擦学行为的影响

利用阴极电弧离子镀技术在316L不锈钢基体上制备了CrN薄膜。采用扫描电子显微镜(SEM)、X射线衍射仪(XRD)、纳米压痕仪对CrN薄膜的形貌、成分和力学性能进行了表征。为了研究Si_3N_4和52100钢对磨副材料对CrN薄膜和316L不锈钢干摩擦行为的影响,在2N、5N、8N三种载荷下,将CrN薄膜和316L不锈钢基体与Si_3N_4陶瓷球和52100钢球分别进行了往复式滑动干摩擦实验。采用扫描电子显微镜观察了磨痕的微观形貌,并对CrN薄膜和316L不锈钢基体的磨损机制进行了分析。结果表明:CrN薄膜表面平整,缺陷较少;CrN薄膜的纳米硬度约为28GPa,弹性模量约为350GPa;与Si_3N_4陶瓷球相比,CrN薄膜与52100钢球摩擦时摩擦因数相对较小(保持在0.7左右)且更加稳定;316L不锈钢的摩擦因数远大于CrN薄膜且波动较大;对磨球为Si_3N_4陶瓷球时,CrN薄膜的主要磨损机制为磨粒磨损,伴有少量的氧化和黏着磨损,316L不锈钢的磨损机制主要为磨粒磨损和塑性变形,伴有少量的氧化和黏着磨损;对磨球为52100钢球时,CrN薄膜的主要磨损机制为黏着磨损,伴有少量的氧化,316L不锈钢的磨损机制主要为黏着磨损,伴有少量的氧化和磨粒磨损。CrN薄膜与两种对磨球的磨损量均小于316L不锈钢基体的磨损量,说明CrN薄膜有效提高了基体的耐磨性。     

基体偏压对AlCrSiN涂层结构及力学性能的影响

AlCrSiN涂层因具有高硬度、优异的耐磨损性及抗高温氧化性而备受关注。为提高AlCrSiN涂层的性能,采用电弧离子镀技术制备了AlCrSiN涂层,研究了基体偏压对AlCrSiN涂层微观组织及力学性能的影响。利用X射线衍射仪(XRD)、扫描电子显微镜(SEM)、显微硬度计、划痕仪及球-盘式摩擦磨损试验机对AlCrSiN涂层的表面形貌、物相组成和力学性能进行表征。研究结果表明:不同基体偏压的AlCrSiN涂层具有B1-NaCl晶体结构和无柱状晶结构;适当提高基体偏压,可细化AlCrSiN涂层的晶粒,提高涂层的表面质量及致密性,从而提高涂层的性能;基体偏压为150V的涂层致密性最好,具有更高的硬度(3 430HV)、结合力(76N)及更好的耐磨损性能。     

结构调制超硬Ti/TiN纳米多层膜的制备及其尺寸效应

使用多弧离子镀技术在高速钢基体上制备了调制周期为5~40 nm的Ti/TiN纳米多层膜,用扫描电子显微镜(SEM)、X射线能谱仪(EDS)、X射线衍射仪(XRD)、纳米压痕仪和划痕仪等手段表征薄膜的微观结构和性能,研究了调制周期对Ti/TiN纳米多层膜性能的影响,并讨论了在小调制周期条件下Ti/TiN纳米多层膜的超硬效应和多弧离子镀技术对纳米多层膜硬度的强化作用。结果表明,与单层TiN相比,本文制备的Ti/TiN纳米多层膜分层情况良好,薄膜均匀致密,没有明显的柱状晶结构,TiN以面心立方结构沿(111)方向择优生长。随着调制周期的减小薄膜的硬度呈现先增大后减小的趋势,并在调制周期为7.5 nm时具有最大的硬度42.9 GPa和H/E值。这表明,Ti/TiN在具有最大硬度的同时仍然具有良好的耐磨性和韧性。Ti/TiN纳米多层膜的附着力均比单层TiN薄膜的附着力高,调制周期为7.5 nm时多层膜的附着力为(58±0.9) N。     

16Cr-2.5Mn高铬白口铁的亚临界热处理研究

研究了亚临界热处理对16Cr-2．5Mn高铬白口铁组织转变和性能的影响，并利用TEM、SEM、XRD和M200磨损试验机分析了其硬化机制和对耐磨性的影响．研究表明：过饱和奥氏体中固溶的Cr和C在亚临界热处理时会以（Cr，Fe）23C6形式析出，残余奥氏体发生了马氏体相变，使合金产生二次硬化；亚临界热处理中，保温时间过长，将导致（Cr，Fe）23C6向M3C原位转变发生，基体组织发生珠光体转变，导致硬度和耐磨性能不同程度降低；残余奥氏体含量为10％左右时，合金获得最高硬度和最佳耐磨性能．     

Surface characterization and mechanical property evaluation of thermally oxidized Ti-6Al-4V

The present study concerns development of a thin and adherent oxide film on the surface of Ti-6Al-4V by thermal oxidation. Thermal oxidation was carried out over a range of temperature between 400 to 600 °C and a time from 25 h to 60 h. A detailed characterization of the surface and cross section of the oxidized surface was carried out by optical/scanning electron microscopy and X-ray diffraction techniques. Finally, the mechanical properties of the oxidized surface in terms of microindentation hardness and wear resistance were evaluated as a function of oxidation parameters. Surface oxidation of Ti-6Al-4V at 600 °C for 36 h offered a defect free oxide scale with improved hardness and wear resistance.     

采用MCECR等离子体溅射方法制备硬碳膜

采用封闭式电子回旋共振(MCECR)等离子体溅射的方法在硅(100)基片上沉积了高质量的硬碳纳米微晶薄膜,膜层厚度约40 nm,采用氩等离子体溅射碳靶.薄膜的键结构采用X射线光电子能谱仪(XPS)分析,纳米结构采用高分辨率透射电子显微镜(HRTEM)分析.本文研究了基片偏压对薄膜的纳米结构、摩擦特性(摩擦系数及磨损率)以及薄膜的纳米硬度的影响.摩擦特性采用POD摩擦磨损仪测试,纳米硬度采用纳米压入仪测试.     

Effects of surface alloying on microstructure and wear behavior of ductile iron

In this research, the effect of austenitic stainless steel cladding on improving the wear behavior of ductile iron was studied. Samples made of ductile iron were coated with steel electrodes (E309L) by manual shielded metal arc welding. The effect of coated layer thickness on microstructure, hardness, and wear resistance of the surface were investigated. Wear resistance of the samples was measured using the pin-on-plate technique. Optical microscopy and scanning electron microscopy were used to investigate microstructure and wear mechanisms. The phases in the interface of both the coating and the substrate were studied by X-ray diffraction. The results showed that a film of white chromium-enriched iron formed at the interface between the substrate and coating which contained iron–chromium complex carbides. It was, therefore, concluded that enhanced properties would be obtained if the coating thickness and the carbides deposited on the surface were reduced. In samples with a thin coating, surface hardness rose to above 1150 HV (five times higher than that of the substrate) and wear resistance increased significantly.     

SiC对自保护明弧高铬堆焊合金性能的影响

采用药芯焊丝自保护明孤堆焊方法制备了系列高铬合金,借助光学显微镜、X射线衍射仪、扫描电镜及湿砂耐磨性实验,研究了SiC含量对其性能的影响.结果表明,SiC显著影响其显微组织形态、尺寸、数量及分布.当SiC含量0％～4％(质量分数,下同)时,堆焊层维织晶粒细化,共晶组织(a-Fe+ M3 (C,B))数量增加,耐磨性下降...     

包铝层和氧化时间对2E12铝合金硫酸阳极氧化及膜层性能的影响

对保留表面包铝和去除包铝的2E12-T3铝合金采用硫酸阳极氧化处理工艺,研究了包铝层和氧化时间对铝合金阳极氧化行为及膜层耐蚀性的影响。采用扫描电子显微镜观察氧化膜的表面以及截面形貌,应用动电位扫描极化曲线和电化学阻抗谱对膜层的电化学性能进行分析。结果表明:两种铝合金表面均能形成具有防护性能的阳极氧化膜,膜层随氧化时间延长而增厚。富铜的第二相颗粒会使得不带包铝的2E12铝合金氧化膜具有更多孔洞缺陷,甚至出现微裂纹。保留包铝的2E12铝合金表面氧化膜更厚,孔洞缺陷少,耐蚀性更好。阳极氧化30min和45min的2E12铝合金阳极氧化膜具有较低的腐蚀电流和较高的多孔层阻抗,耐蚀性好。